Fixed coaxial shaft for a hydraulic unit

ABSTRACT

A fixed coaxial shaft of a hydraulic unit is provided including a body having a first end and a second opposite end. A plurality of first splines is formed in an exterior surface of the body adjacent the first end and a plurality of second splines is formed in the exterior surface of the body adjacent the second end. The plurality of first splines and the plurality of second splines are substantially identical. The body of the shaft has an outer diameter of about 0.640±0.0005 inches (1.626±0.0013 centimeters), an inner diameter of about 0.517±0.010 inches (1.313±0.0254 centimeters), and an overall length of about 2.678±0.005 inches (6.802±0.0127 centimeters).

BACKGROUND OF THE INVENTION

Exemplary embodiments of this invention generally relate to an integrated drive generator, and more particularly, to a fixed shaft of a hydraulic unit of an integrated drive generator.

Aircrafts currently rely on electrical, pneumatic, and hydraulic systems for secondary power. A typical electrical system utilizes an integrated drive generator (IDG) coupled to each engine to provide a fixed frequency power to the distribution system and loads. One type of IDG includes a generator, a hydraulic unit, and a differential assembly arranged in a common housing. The differential assembly is operably coupled to a gas turbine engine via an input shaft. The rotational speed of the input shaft varies during the operation of the gas turbine engine. The hydraulic unit cooperates with the differential assembly to provide a constant speed to the generator throughout engine operation.

Due to packaging constraints, components of the hydraulic unit, such as nested, coaxial, variable and fixed shafts must be redesigned.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment of the invention, a fixed coaxial shaft of a hydraulic unit is provided including a body having a first end and a second opposite end. A plurality of first splines is formed in an exterior surface of the body adjacent the first end and a plurality of second splines is formed in the exterior surface of the body adjacent the second end. The plurality of first splines and the plurality of second splines are substantially identical. The body of the shaft has an outer diameter of about 0.640±0.0005 inches (1.626±0.0013 centimeters), an inner diameter of about 0.517±0.010 inches (1.313±0.0254 centimeters), and an overall length of about 2.678±0.005 inches (6.802±0.0127 centimeters).

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a generator system of an aircraft;

FIG. 2 is a cross-sectional schematic view of an example of an integrated drive generator (IDG);

FIG. 3 is a cross-sectional view of an example of a hydraulic unit of an integrated drive generator;

FIG. 4 is a perspective view of a fixed coaxial shaft configured for use in a hydraulic unit according to an embodiment of the invention;

FIG. 5 is a top view of the fixed coaxial shaft of FIG. 4 according to an embodiment of the invention;

FIG. 6 is a cross-sectional view of the fixed coaxial shaft taken along line A-A of FIG. 5 according to an embodiment of the invention;

FIG. 7 is a detail view of section B of the fixed coaxial shaft of FIG. 6 according to an embodiment of the invention; and

FIG. 8 is a cross-sectional view of one of the plurality of splines taken along line C-C of FIG. 6 according to an embodiment of the invention.

The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, an example of a generator system 10 is schematically illustrated. The system 10 includes a gas turbine engine 12 that provides rotational drive to an integrated drive generator (IDG) 16 through an accessory drive gearbox 14 mounted on the gas turbine engine 12. The accessory drive gearbox is coupled to a spool of the engine 12, and the speed of the spool varies throughout the entire engine operation.

An example of an IDG 16 including a housing 18 is shown in FIG. 2. In the illustrated embodiment, the IDG 16 includes an input shaft configured to receive rotational drive from the accessory drive gearbox 14. The rotational speed of the input shaft varies depending upon the operation of the engine. To this end, a hydraulic unit 32 cooperates with the differential assembly 28 to convert the variable rotational speed from the input shaft to a fixed rotational output speed to the generator 24.

Referring now to FIG. 3, an example of a hydraulic unit 32 of the IDG 16 is illustrated in more detail. The hydraulic unit 32 includes a variable displacement hydraulic pump 34 and a fixed displacement hydraulic motor 36. The pump 34 and motor 36 have respective cylinder blocks 38 and 40 which are arranged for rotation about a common axis A within a housing 42 on opposite sides of a stationary port plate 44 of the hydraulic unit 32. The port plate 44 is formed with apertures 46 through which hydraulic fluid communication between the pump 34 and the motor 36 is established during normal operation of the hydraulic unit 32. A biasing mechanism 48 resiliently biases the cylinder blocks 38, 40 in the direction of the port plate 44.

The operation of the hydraulic unit 32 in an IDG 16 of an aircraft involves transmission of torque from an engine of the airplane to an input, which rotates the input shaft 50 of the hydraulic unit 32 about axis A. The cylinder block 38 of the pump 34 is connected to the input shaft 50 for rotation therewith. Pistons 52 within the cylinder block 38 of the pump 34 are displaced during this rotation an amount which is a function of the setting of a variable swash plate 54 of the pump 34.

Hydraulic fluid under pressure from the pump 34 is delivered to the hydraulic motor 36 through the port plate 44 for rotating the cylinder block 40 and an output shaft 56 to which it is fixedly connected. A fixed coaxial shaft 60 is arranged coaxially with and is coupled to the output shaft 56 to impart the rotation of the output shaft to an adjacent component, such as a differential (not shown) for example. The swash plate 58 of the motor 36 is fixed so that the operating speed of the motor 36 is a function of the displacement of the pump 34. The rotary output from output shaft 56 is added to or subtracted from the rotary motion from the engine through the conventional differential gearing of an IDG 16 for operating an electrical generator at a substantially constant rotational speed. That is, since the speed of the rotation from the airplane engine to the input 50 of the hydraulic unit 32 will vary, the position of the variable swash plate 54 is adjusted in response to these detected speed variations for providing the necessary reduction or increase in this speed for obtaining the desired constant output speed to the generator. During normal operation, there is a hydrostatic balance of the cylinder blocks and port plate. Although the hydraulic unit illustrated and described herein refers to the variable unit as a pump and the fixed unit as a motor, hydraulic units having other configurations, such as where the variable unit functions as a motor and the hydraulic unit operates as a pump for example, are within the scope of the invention.

Referring now to FIGS. 4-8, a fixed coaxial shaft 60 of the hydraulic unit 32 according to an embodiment of the invention is illustrated in more detail. The shaft 60 includes a substantially elongated non-uniform body 62 having a first end 64, a second, opposite end 66, and a substantially hollow interior 68 that extends between the first and second ends 64, 66. The overall length of the body 62 is about 2.678±0.005 inches (6.802±0.0127 centimeters). In one embodiment, the outer diameter of the body is about 0.640±0.0005 inches (1.626±0.0013 centimeters). In addition, the inner diameter of the body may be about 0.517±0.010 inches (1.313±0.0254 centimeters). The first end 64 of the shaft 60 may include a chamfer 70 extending outwardly at about a 60° angle such that the inner diameter at the first end 64 of the body 62 is about 0.580±0.010 inches (1.473±0.0254 cm). Similarly, a chamfer 72 may be formed in the second, opposite end 66 of the body 62. In one embodiment, the chamfer 72 at the second end 66 is substantially identical to the chamfer 70 arranged at the first end 64.

A plurality of first splines 76 is formed in an exterior surface 74 of the body 62 adjacent the first end 64, and a plurality of second splines 78 is formed in the exterior surface 74 of the body 62 adjacent the second end 66 thereof. In one embodiment, the plurality of first splines 76 and the plurality of second splines 78 are substantially identical. The plurality of first splines and second splines 76, 78 may be constructed as detailed in Table 1.

TABLE 1 External Spline Dimensions Data for External Involute Splines Type Fillet Root Side Fit Class D Pitch Diameter .7500 in No. of Teeth 18 Pitch Fraction 24/48 Base Circle Diameter .6495 in Pressure Angle 30° Max Form Diameter  .708 in Min Dim. Over Two Wires .8600 in Wire Size 0.08 Major Diam .792 + .000 − .005 in Minor Diam .667 + .000 − .014 in Additional Reqs when Max effective size is not gaged Max Profile Variation .0010 in Max Lead Variation .0003 in Circular Tooth Thickness Max Actual .0583 in Circular Tooth Thickness Min Actual .0568 in Max Diam Over Two Wires .8623 in Max Index Variation .0015 in

As shown, a first end 80 of the plurality of first splines 76 and a first end 82 of the plurality of second splines 78 are spaced from the adjacent first and second ends 64, 66 of the body 62, respectively, by a distance of about 0.145±0.005 inches (0.368±0.0013 centimeters). In one embodiment, the distance from the first and second ends 64, 66 to an opposite end 84, 86 of each of the plurality of first and second splines 76, 78 is about 0.575±0.010 inches (1.46±0.0254 centimeters). In addition, a distance from each of the first and second ends 64, 66 to a midpoint M of the adjacent first and second splines 76, 78 may be 0.360±0.030 inches (0.914±0.076 centimeters).

A radius, best illustrated in FIG. 7, may be formed at the interface of the exterior 74 of the body 62 and the ends 80, 84, 82, 86 of the plurality of first and second splines 76, 78. In one embodiment, the radius is about 0.030±0.010 inches (0.076±0.0254 centimeters). In addition, a chamfer 90 may be formed at the first ends 80, 82 of the plurality of first and second splines 76, 78. The chamfer 90 may have a width, parallel to a longitudinal axis X of the shaft 60, of about 0.018±0.010 inches (0.046±0.0254 centimeters), and may extend at 45°±5°.

Referring now to FIG. 8, a cross-section of one of the plurality of first and second splines 76, 78 is illustrated in more detail. In the illustrated, non-limiting embodiment, the distance between the midpoint M and an end 80, 84, 82, 86 of each of the first and second splines 76, 78 is about 0.215 inches (0.546 centimeters). The periphery of each of the splines 76, 78 extending between the midpoint M and the ends 80, 84, 82, 86 thereof includes a radius of about 10 inches. A first point P on the periphery of the first and second splines 76, 78 is located at a distance parallel to the longitudinal axis X of about 0.200 inches (0.508 centimeters) from the midpoint M and at a vertical distance from the midpoint M of about 0.0020±0.0005 inches (0.005±0.001 centimeters). A second point R on the periphery of the first and second splines 76, 78 is located at a distance from the midpoint M, parallel to the longitudinal axis, of about 0.100 inches (0.0254 centimeters) and at a vertical distance of about 0.0005±0.0003 inches (0.001±0.00076 centimeters) from the midpoint M.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

What is claimed is:
 1. A fixed coaxial shaft of a hydraulic unit, comprising: a body having a first end and a second opposite end and a plurality of first splines formed in an exterior surface of the body adjacent the first end and a plurality of second splines formed in the exterior surface of the body adjacent the second end, the plurality of first splines and the plurality of second splines being substantially identical, wherein the body has an outer diameter of about 0.640±0.0005 inches (1.626±0.0013 centimeters), and inner diameter of about 0.517±0.010 inches (1.313±0.0254 centimeters), and an overall length between the first end and the second end of about 2.678±0.005 inches (6.802±0.0127 centimeters).
 2. The fixed coaxial shaft according to claim 1, wherein an interface between the plurality of first splines and the exterior surface of the body and an the interface between the plurality of second splines and the exterior surface of the body has a radius of about 0.030±0.010 inches (0.076±0.0254 centimeters).
 3. The fixed coaxial shaft according to claim 1, wherein a first end of the plurality of first splines and a first end of the plurality of second splines are spaced away from the first end and the second end of the body, respectively, by a distance of about 0.145±0.005 inches (0.368±0.0013 centimeters).
 4. The fixed coaxial shaft according to claim 2, wherein a chamfer is formed in the first end of the plurality of first splines and the first end of the plurality of second splines, the chamfer having a width parallel to a longitudinal axis of the shaft or about 0.018±0.010 inches (0.046±0.0254 centimeters) and extends at an angle of about 45°±5°.
 5. The fixed coaxial shaft according to claim 2, wherein a second end of the plurality of first splines and a second end of the plurality of second splines are spaced away from the first end and the second end of the body, respectively, by a distance of about 0.575±0.010 inches (1.46±0.0254 centimeters).
 6. The fixed coaxial shaft according to claim 1, wherein a midpoint of the plurality of first splines and a midpoint of the plurality of second splines are spaced away from the first end and the second end of the body, respectively, by a distance of about 0.360±0.030 inches (0.914±0.076 centimeters).
 7. The fixed coaxial shaft according to claim 1, wherein the plurality of first splines and the plurality of second splines are constructed in accordance with Table
 1. 8. The fixed coaxial shaft according to claim 1, wherein a periphery of the first splines and the second splines includes a radius, such that a horizontal distance between a midpoint and a first point on the periphery is about 0.200 inches (0.508 centimeters) and a vertical distance between the midpoint and the first point is about 0.0020±0.0005 inches (0.005±0.001 centimeters).
 9. The fixed coaxial shaft according to claim 8, wherein a second point is arranged on the periphery of the first splines and second splines between the midpoint and the first point, wherein a horizontal distance between a midpoint and a second point is about 0.100 inches (0.0254 centimeters) and a vertical distance between the midpoint and the first point is about 0.0005±0.0003 inches (0.001±0.00076 centimeters).
 10. The fixed coaxial shaft according to claim 1, wherein a chamfer is formed in the first end of the body, the chamfer extending outwardly at about 60° such that an inner diameter at the first end of the body is about 0.580±0.010 inches (1.473±0.0254 centimeters).
 11. The fixed coaxial shaft according to claim 1, wherein a substantially identical chamfer is formed at the second end of the body. 